If we are using the Apple toolchain on MacOS X, we must use the
newer runtime and not the old GCC 4.2 fork, in order to get the
C++11 library features (such as std::shared_ptr).
AGMG is now under a closed-source license, meaning that results
obtained with this solver is not freely reproducible by others.
Its use is therefore discouraged.
As of version 2.3, the DUNE AMG parts are competitive, so there
is a free and open alternative.
